Find ff(x) when f(x)=5-3x

Question

Having trouble solving this

Answer 1

Another way to format ff(x) is f(f(x)).

Whenever there is something inside the parentheses, like f(3), you replace x for 3 in the function.

So f(3) = 5 - 9 = -4

Therefore, we can do the same with f(f(x))

f(x) = 5 - 3x

so f(f(x)) is f(5 - 3x).

f(5 - 3x) = 5 - 3(5 - 3x) = 5 - 15 + 9x = 9x -10

f(f(x)) = 9x - 10